When tightening rotatable fastening elements by use of power tools in controlled power tool systems, a desired torque value has to be fed in to the operation control unit of the power tool for a preselected work. This is usually done by means of a keyboard in connection to the control unit, by directly inputting the numerical desired torque value. Another usual technique is a flip-setting device, in which the desired torque value is preset by pushing a button or turning a knob in connection to the operation control unit. Subsequently the power tool is placed in engagement with the preselected fastening element and operated, by pushing the start button for operation of the electric motor, for tightening of the fastening element. Usually the power tool system is provided with surveillance means, such that the motor automatically switch off the tightening when the desired torque value is approached, and the final tightening of the fastening element to the desired torque value is carried out by slow operation of the electric motor. According to the state of the art, torque wrenches are previously known that are used for inspection or tightening by hand.
The known methods and apparatuses for presetting a desired torque value as well as tightening rotatable fastening elements to a desired torque value, are time-consuming and also relatively slow, considering also that one has to reset the torque value on a keyboard or a flip-setting device each time the desired torque value shall be altered for carrying out a new work. Hence, a problem with the prior art technique is that the tightening work is that every single work operation has to be planned in advance, by separately presetting the present torque value for each fastening element that should be tightened. Hence, there is no freedom to work in an unscheduled way, randomly chosen, when tightening a plurality of fastening elements with different desired torque values, which fastening elements are present on a construction ahead of the worker.